The present invention relates to medical devices in general, and in particular to ablation systems for revascularizing occluded blood vessels.
A common technique for treating partially or totally occluded cardiac vessels is cardiac bypass surgery. With this procedure, a surgeon harvests a vessel from another part of the patient""s body. The harvested vessel is grafted to healthy sites in the cardiac vessels in order to direct blood flow around a blockage or around unhealthy tissue of the heart muscle. For example, a portion of the saphenous vein may be used, resulting in what is referred to as a saphenous vein graft or SVG.
However, SVG""s also may become occluded within a few years of being grafted onto the heart muscle. The material that occludes SVG""s can be more loosely organized and brittle than the material that occludes native cardiac vessels. As a consequence, treating occluded SVG""s can be more difficult because the occluding material tends to break off and can flow downstream where it becomes trapped or causes a blockage.
One method of treating vein graft lesions is described in U.S. Pat. No. 5,681,336. That patent discloses a system of ablating vein graft lesions by use of proximal and distal balloons that isolate the treatment area. Ablated material is aspirated. Infusion of liquid may be used to maintain vascular pressure and prevent the grafted vein from collapsing during aspiration. Specially designed burrs are used to abrade a lesion in the vein, and the abraded material is aspirated through a catheter that extends into the treatment area. Nevertheless, there is some concern that not all of the ablated material will be aspirated so that, following treatment, such material may be carried downstream.
The present invention provides an improved system for ablation of blood vessel lesions using both aspiration for removal of ablated material and infusion directed distally (frontally) for washing the treated area. The amount of frontal infusion for washing purposes is carefully controlled so that the ablated material still flows proximally (rearward) into an aspiration catheter. The proximal end portion of the area to be treated can be isolated by use of a balloon or other blocking device. The distal portion of the treatment area also may be blocked, to assist in directing the forward flow of the infusion liquid, or the flow rate of infusion liquid can be carefully controlled so as not to direct ablated material distally away from the treated area. For example, the respective degrees of aspiration and frontal infusion can be controlled to assure that all distally directed infusion liquid is aspirated proximally, carrying with it any loose material.
The infusion liquid can be conveyed through an axial bore of a flex shaft to an ablation burr movable along a guide wire. The burr can be provided with passages for expelling the infusion liquid, including passages directed distally along the guide wire and/or passages through the distal portion of the burr itself. Additional passages for the infusion liquid can be directed transversely of the length of the guide wire for washing the wall of the treated graft. Such transverse passages can be directed primarily transversely but angled proximally for controlling the direction of the flow and ablated particles. Aspiration can be through an outer tube or sheath surrounding the burr-driving flex shaft. The relative amounts of distal infusion, transverse infusion, and aspiration can be controlled to assure that all or essentially all of the infusion liquid and particles carried thereby are ultimately directed proximally to the opening of the aspiration tube.
In another embodiment, the frontal or distal infusion can be through one or more passages in the outer sheath surrounding the flex shaft, or in a distally extending portion of the flex shaft. For infusion through the distal tip of the ablation burr, a valve member can be provided on the guide wire for selectively sealing and opening the distal infusion passage. Different configurations of infusion passages may be used to assure a thorough washing of the treated area.
Distal infusion also can be obtained by a specially designed burr having arcuate or helical grooves which tend to direct the flow of infusion liquid proximally or distally depending on the direction of rotation of the burr. In this construction, the burr can be alternately rotated in one sense and the other sense to first direct infusion liquid distally for washing, then proximally for assuring removal of loose material carried by the infusion liquid.